Consumer products including food products, cleaning products, deodorizers and the like have a shelf life determined by the length of time the components of the product resist change to environmental influences. For example, food products have a given shelf life based on their ability to resist chemical or physical changes due to contact with air, heat and other influences in the environment. Many consumer products are date stamped to provide the user with an indication of the shelf life of the product. The shelf life may be relatively short such as a few days or may be relatively lengthy such as a few months. Date stamping of consumer products provides the user with some indication of when the product may no longer be useful for its intended purpose.
Quite often, date stamps are printed inconspicuously on the product package. It is sometimes difficult to read the date stamp and in some cases even to find the date stamp because it may be printed anywhere on the package. Date stamping is particularly problematic for products which have a relatively long shelf life because such products tend to get stored in obscure recesses of a storage area, such as a food cabinet or refrigerator. If the product is not used often, the consumer is often unaware that the expiration date is shortly forthcoming or has even passed.
There have been attempts to provide a visible indication of when the useful life of a product has expired. So called life time indicators are employed for food products such as are disclosed in U.S. Pat. Nos. 2,671,028; 3,751,382; and 3,942,467. These indicators typically work through chemical reactions initiated or increased in rate by exposure to high temperatures. Other lifetime indicators rely on diffusion of a component through a traditional wick or membrane as disclosed in U.S. Pat. Nos. 3,414,415; 3,479,877 and 3,768,976, each of which is incorporated herein by reference.
Examples of other such products which incorporate useful life indicators include, for example, certain toothbrush wear indicators which are based on the diffusion of a dye out of the bristles. When the color of a select group of bristles disappears, the user is aware that the toothbrush may or should be discarded and replaced. Another example is found in a deodorizer product having a timer based on the evaporation of a solvent from a polymer gel and subsequent shrinkage of the gel.
The timing indicators mentioned above suffer from one or more disadvantages which makes their universal applicability to a wide range of packaged products problematical. Such disadvantages include a) the timing mechanism is part of the product (e.g. a deodorizer) and is therefore limited to employment with that product or that class of products, b) the timing mechanism is inaccurate or cannot be controlled to accommodate a wide range of product shelf lives, c) the timing mechanism is expensive and/or d) has a limited range of measurement.
U.S. Pat. No. 6,269,764 discloses a timing device which overcomes at least some of the problems mentioned above. The device disclosed in that patent is in the form of an inverted U-shaped tube with at least one of the opposed ends having opposed reservoirs for storing a reactant and an indicator with a wick employed to enable the reactant to contact the indicator thereby initiating a color change over a preselected period of time.
It would be an advance in the art of providing visible indicators for determining when a product should be replaced or rejuvenated if a cost efficient and effective shelf life indicator could be provided which provides a clear and distinct visible indication of when a product should be replaced or rejuvenated and does so without employing a wicking material so as to reduce the cost of the device.